The failure of tools used in oil and gas drilling, in the majority of cases, can be attributed to a failure of either seals or bearings. This patent application will address premature bearing failure.
There are two types of thrust bearings currently used is oil and gas drilling applications; thrust bearings having polymer plastic cages and thrust bearings having metallic cages. Polymer plastic bearings have a cage formed by two retainers joined together by means of rivets or adhesives to form a cage. The cage has solid dividers or cross bars that form radial pockets in which the rollers are positioned. The first retainer and second retainer have openings through which a radius portion of the rollers protrude. Polymeric cages are not preferred for high temperature applications as many of the materials can easily degrade at high temperatures. Also, on larger sizes the thickness of the plastic must be increased in order to make the cage sufficiently rigid.
Metallic cage bearings have a cage that is formed from a solid disc with radial slots that are open on the outer end. In between the radial slots are solid dividers. Rollers are retained in the radial slots by pressing a ring around the outside periphery of the disc. With this design, the solid dividers must be made sufficiently thick to ensure a reasonably rigid design.
The common items between both of the above designs are that they both include dividers between each roller pocket. These dividers provide a place for abrasive particles to become lodged and rub on the rolling elements of the bearing. This can have a detrimental effect on the life of said bearing.
The bearings are immersed in lubricant. The lubricant has a limited ability to “wash” abrasive grit out from between the rollers. Eventually, a build up of abrasive grit occurs and one or more of the rollers becomes jammed against the cage. The useful life of a thrust bearing, in the absence of overloading and other abusive situations, is currently around 80 hours. A drilling tool is, therefore, sent for servicing after 80 hours. Upon inspection after 80 hours, the bearings are usually in need of replacement.